1. Field of the Invention
The present invention relates to a film deposition apparatus for depositing a film on a substrate by supplying a reaction gas to an upper surface of the substrate.
2. Description of the Related Art
In a semiconductor fabrication process, a film deposition method has been known that is called an atomic layer deposition (ALD) method or a molecular layer deposition (MLD) method where after a first reaction gas is adsorbed on an upper surface of a semiconductor wafer (simply referred to as wafer hereinafter) serving as a substrate, a second reaction gas is adsorbed on the upper surface, so that one or more atomic (or molecular) layers are produced through chemical reaction of the first and the second reaction gases on the surface of the wafer, and then this cycle is repeated plural times. Because a thickness of the thin film can be controlled at higher accuracy by the number of the cycles and the deposited film can have excellent uniformity across the wafer, this deposition method is thought to be promising as a film deposition technique that can address further miniaturization of semiconductor devices.
Such a film deposition method may be preferably used, for example, for depositing a dielectric material to be used as a gate insulator. When a silicon oxide film is deposited as the gate insulator, a bis (tertiary-butylamino) silane (BTBAS) gas or the like is used as a first reaction gas (source gas) and ozone (O3) gas or the like is used as a second gas (oxidation gas).
In order to carry out such a deposition method, use of a single-wafer deposition apparatus having a vacuum chamber and a shower head at a top center portion of the vacuum chamber has been under consideration. In such a deposition apparatus, the reaction gases are introduced into the chamber from the top center portion, and unreacted gases and by-products are evacuated from a bottom portion of the chamber. When such a deposition chamber is used, it takes a long time for a purge gas to purge the reaction gases, resulting in an extremely long process time because the number of cycles may reach several hundred. Therefore, a deposition method and apparatus that enable high throughput is desired.
Under these circumstances, there have been proposed film deposition apparatuses having a vacuum chamber and a rotation table that holds plural substrates along a rotation direction, where the reaction gases are alternately supplied to the plural substrates by rotating the rotation table. For example, Patent Document 1 listed below discloses a film deposition apparatus including a process chamber divided into plural process spaces to which different reaction gases are supplied from corresponding ceiling portions, and a rotation table that allows the substrates placed thereon to alternately pass through the plural process spaces.
In addition, Patent Document 2 discloses a film deposition apparatus including, for example, two reaction gas nozzles that eject different reaction gases toward a rotatable table on which plural substrates are placed. In this film deposition apparatus, the plural substrates can alternately pass through and below the reaction gas nozzles by rotating the rotatable table, thereby alternately supplying the reaction gases to the substrates. Such a film deposition apparatus can improve production throughput because a purge step for purging the reaction gases is not necessary and the plural substrates can be processed in one run.
However, there may be a problem in that a gas concentration is varied along a radius direction of the rotatable table in such a film deposition apparatus where the substrates are exposed to the reaction gases by rotating the rotatable table. This is partly because tangential speeds of the rotatable table become higher toward a circumferential edge from a rotation center portion of the rotatable table, which affects in an unexpected manner a flow pattern of the reaction gases flowing over the rotatable table.
In the film deposition apparatus disclosed in Patent Document 2, where a purge gas is preferably supplied in order to separate the reaction gases supplied from the corresponding reaction gas nozzles, because an amount of the purge gas flowing into areas where the reaction gases are supplied may vary depending on process conditions, this may lead to a varied gas concentration along the radius direction of the rotatable table.
Moreover, even when the same reaction gas is supplied as a first reaction gas and a second reaction gas, if a target thickness of the film to be deposited and the process conditions such as a rotation speed of the rotatable table, a process pressure, and the like are changed, the flow pattern of the reaction gas may be easily changed, which may degrade thickness uniformity of the film. Because further improvement in film uniformity is desired in view of recent demands for further reduced patterns, a film deposition apparatus capable of improving a reaction gas concentration along a radius direction of a substrate and addressing changes in the process conditions has been desired.
Patent Document 1: Japanese Patent Publication No. 3,144,664 (FIGS. 1, 2, claim 1)
Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2001-254181 (FIGS. 1 and 2)